As mobile devices have been increasingly developed, and the demand for such mobile devices has increased, the demand for secondary batteries has also sharply increased. Among such secondary batteries is a lithium secondary battery exhibiting high energy density and operating voltage and excellent charge retention and service-life characteristics, which has been widely used as an energy source for various electronic products as well as mobile devices.
However, various kinds of combustible materials are contained in the lithium secondary battery. As a result, the lithium secondary battery may be heated or explode due to the overcharge of the battery, the overcurrent in the battery, or external physical impact. That is, the safety of the lithium secondary battery is very low. Consequently, safety elements, such as a positive temperature coefficient (PTC) element and a protection circuit module (PCM), to effectively control an abnormal state of the lithium secondary battery, such as the overcharge of the lithium secondary battery or the overcurrent in the lithium secondary battery, are mounted to a battery cell in a state in which the safety elements are connected to the battery cell.
The lithium secondary battery has been used in various applications. Typically, the lithium secondary battery is used as a power source of a laptop computer. A battery pack mounted in a laptop computer requires high power and large capacity. To this end, a conventional cylindrical battery pack including a plurality of cylindrical battery cells has generally been used. In recent years, however, the size of a laptop computer has been reduced, and therefore, there is a high necessity for a slim type battery pack.
Therefore, there is a high necessity for a pack case in which pouch-shaped battery cells are used to manufacture a slim type battery pack, thereby increasing capacity of the battery pack, simplifying a manufacturing process of the battery pack, and minimizing the total size of the battery pack.
Also, a short circuit may occur due to contact between electrode terminals of the battery cells and components of the protection circuit module or flow of electrolyte leaking from one or more of the battery cells to the protection circuit module. Therefore, there is a high necessity for a pack case configured to have a structure that is capable of solving the above problems.